add effect brightness to both layouts.
then add 2 global variables - brightness and transition
on first layout on layout started - set brightness variable to 100 and transition to 0
on first layout when you want to change layouts instead set this:
set variable transition to 1
make an event that does this:
if transition = 1
subtract from brightness 1
set effect brightness param 0 to brightness (variable)
(subevent)
if(brightness=0) - > go to layout 2
and on layout 2 - set variable brightness = 0 on start
if ( transition = 1 )
brightness +1
set effect brightnes param 0 to brightness (Variable)
(subevent)
if(brightness=100) transition = 0
something like this should work, around 1-2 sec fade, depending on your fps.